This invention relates to electric motors and in particular, to a brush cage assembly for use with a fractional horsepower electric motor.
Previously, plastic brush cages have been used for guiding brushes to the commutator of an electric motor. Typically, these brush cages are mounted in apertures in a metal bracket which also supports a bearing for the motor shaft. These cages are usually held in place by two rivets passing through holes in the brush cage and in the bracket. The cost of the rivets and time taken to set the rivets adds to the overall cost of the motor. Alternative schemes have used glue to fasten the brush cage in place but the cost of the glue which must resist aging under extreme temperatures and vibration conditions means that this method is not a significant cost reduction.
Another problem facing users of brush cage assemblies is how to retain the brush within the brush cage and make a good electrical connection between the brush and the supply lead. For high current applications, it is necessary to provide brushes with shunts but for low current applications, the brush spring is often used for the electrical contact with the brush with the cap for the brush cage acting as a terminal plate connecting the supply lead to the brush spring. However, prior art designs usually involve deforming the cap or brush cage insert or a lateral movement of the cap to close the brush cage and capture the brush spring within the brush holder. As the spring bears against the terminal plate or cap, the cap must be securely fastened to the brush holder. However, as the spring is being compressed as the lateral movement or deforming process takes place, there is a real danger of damage being caused to the spring. Hence, there is also a need for a simple yet effective conductive closure for a brush holder for shuntless brushes.
The present invention, in one aspect thereof, provides a cost reduction by halving the number of rivets used to fasten the brush cage to the bracket. This is achieved by using a brush holder which has a projection arranged to bear against an inner surface of the support bracket and is arranged to be secured to the bracket by a single fastener.
Accordingly, the present invention provides a brush holder assembly, for use in a fractional horsepower universal motor, the assembly comprising: a brush holder having a through hole for slidably receiving a carbon brush and a brush spring; a terminal for connecting the brush to a supply lead; a cap for closing one end of the through hole thereby capturing the brush spring within the brush holder between the cap and the brush, wherein the brush holder has a flange for bearing against an outer surface of a support bracket and the brush holder has a projection arranged to bear against an inner surface of the support bracket and is arranged to be secured to the bracket by a single fastener.
Preferably, the support bracket has an aperture sized to receive the brush holder and the brush holder is fitted to the bracket by inserting the brush holder through the aperture in the bracket in a first direction so that the flange bears against the outer surface of the bracket and then moving the brush holder in a second direction orthogonal to the first direction so that the projection bears against the inner surface of the bracket.
Preferably, the brush holder has two passageways extending in the same direction as the brush through hole, each having a step therein and the cap has two arms, each having a lanced and raised portion, the arms extending along the passageways with the raised portions engaging the steps preventing the withdrawal of the arms from the passageways.
By these additional features, the closure member which may also be the terminal plate, is fastened to the brush holder by a simple axial movement which compresses the brush spring at the same time. Thus the brush spring is compressed and the terminal plate is fixed to the brush holder by a single axial movement.
These and other features and advantages of this invention will become apparent from the following description of preferred embodiments of the invention, offered as an example only.